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Tuesday, May 28, 2013

Removing the danger from the power supply of my RepRap

For a long time my printers power supply was in prototype mode ;-) which means that the mains supply cables are mounted dirctly to the PSU terminals, no fuse no protection from being touched. Risk of electronic shock was high.

The power supply i'm using is the Meanwell SP-320 24V.

I decided to use a power inlet module with 2-pole swich and integrated fuse holder for maximum safety. The module i am using is the Bulgin BZH01/Z0000/11 fused Power Inlet Module with illuminated 2-pole switch. (Farnell: 9997237).

The images showing the result. For 230V supply voltage a slow 2.5A 5x20mm fuse is recommended.

The protective cover is available at Thingiverse.

Tuesday, May 21, 2013

Connecting printrbot's printrboard with my RepRap graphics LCD Controller


Based on an article in
The Printrboard is a based on the Teensylu which is itself a derivative of the Sanguinololu; the main difference is the use of the AT90USB1286 instead of the Atmel ATmega1284P.

Wiring of the RepRap Graphics LCD Controller with Fan Output

The Controller comes with a 20pin ribbon cable. The Table shows how to connect it.

PrintrBoard PCB

Ribbon cable wire number
Printrboard Pin Label
Marlin Pin
Marlin Pin









Firmware changes will follow...

Thursday, May 16, 2013

Testing my RepRap graphics LCD Controller

PCB Prototyping for my Indiegogo Campaign

RepRap Graphic LCD Controller with Fan Output

I'm having a campaign of that controller at Indiegogo. Here i'm showing a little bit about the prototypes on that. If you like it, think about supporting my campaign and order one of these controllers. They work with Sanguinololu, Melzi & RAMPS.

Bare LCD Controller PCBs & Sanguinololu

PCB with solderpaste

SMDs populated

Populated PCB connected to Sanguinololu 1.3a

The Video

Many users asked for an RAMPS adapter, here impressions of it. It will be plugged on the AUX headers on RAMPS.

Sunday, May 12, 2013

Research on MOSFET switching

My article in the RepRap Wiki i tried to explain what is happening on the lines when the MOSFET is switching. I showed in Simulation, that heavy spikes can occur, when the freewheeling diode is missing.
I talked to another user reporting large spikes on the thermistor inputs of the ADC caused by cross coupling of the spikes on the heater cables to the thermistor cables.
With the upcoming trend of also doing PID tuning for the heated bed it will become more and more important to reduce these spikes to a minimum.

The pictures show the voltage across the MOSFET from Drain to source when switching the hotend/heatbed on and off.

Here is an example how it could look like if the switching circuit is well designed. The overshoot is only approx. 4V compared to 50-250V (!!) in conventional designs. All measurements were done on my esasy electronics.

Bad Example

Here is an example of a switching a hotend without freewheeling diode. Large spike occur during switching off the hotend. The overshoot is approx 30V above the 12V supply voltage. This means if a FET with lower voltage rating as 60V was used it will be killed sooner or later by these spikes!

Bad example of hotend switching

Let's make it better

Switching the Heatbed with freewheeling Diode

The heatbed has some minimal overshoot but for the swiched current of approx. 9A it is still an excellent behavior.

Heatbed switching from on -> off state

Heatbed switching from off -> on state

Switching the Hotend

The hotend shows nearly no overshoot and smooth switchin, which is excellent.
Hotend switching from on -> off state

Hotend switching from off -> on state

Saturday, May 11, 2013

Testing the 205W Kapton heater foil from a RepRap-Forum member

Currently I'm switching from 12V to 24V supplyvoltage on my MendelMax. As first step i ordered a 24V 200W Kapton heating foil from a reprap forum member (Le-Seaw). It has an embedded EPCOS Thermistor, the cables are approx. 0.5m long.


  • Supply voltage 24V
  • Power rating 205W
  • Cable length approx. 0.5m
  • Embedded EPCOS Thermistor 100k (ErikZalm/Marlin Thermistor type 1)
  • Size 205x205mm²


I mouted this to a 230x230x2mm³ aluminium plate

230x230x2mm³ Aluminium Plate
Kapton Heater with EPCOS Thermistor
Some shrink tubing over the cables gives stability
Finally added Molex connectors and protective fabric hose


Current consumption

I'm operating the board with my easy electronics at 24V from a Meanwell SP320-24. Current consumption is 9.6A which gives 230W which is 12% out of spec.


It heats up in less than 4 min. to 95°C mounted on a 2mm aluminium plate (230x230x2mm³) mounted on a wooden plate with a 1mm silicone interposer. Temperature reading in Marlin is 93.5°C.


It looks and feels like a high quality product. It is easy to applicate to a aluminium plate. Cables are a little bit short and very stiff. Thermistor gives accurate board temperatures when configured in Marlin as Type 1 thermistor.

What can be improved?

  • Really flexible cables, may be four for the heater with smaller diameter
  • Longer cables, at least 75cm better 1m
  • Reduce the power a little bit to reduce the powersupply load. With 230W a 13A powersupply plus 2 Extruders is bejond its limits. 7.5A (180W) could be a good compromise.
That's all for now....

Thursday, May 9, 2013

My first Blog Entry

Welcome to my first blog entry. Just finished the logo for the blog, i hope you like it.

I'm mainly an electronics designer, this is the reasen why my blog will probably focus more on electronics development as on the mechanics. Currently I'm making some trials with CAD software for construction but the results are far away from being usable.

Now let's wait and see which things will come....